Breast cancer is the most frequent cancer among women both in developed and developing countries, with an estimated 1.38 million new cancer cases diagnosed in 2008 worldwide (23% of all cancers). Incidence rates vary from 19.3 per 100,000 women in Eastern Africa to 89.7 per 100,000 women in Western Europe. Rates are high (greater than 80 per 100,000) in all developed regions of the world except in Japan. However, rates are low (less than 40 per 100,000) in most of the developing regions. The range of mortality rates is much smaller (approximately 6-19 per 100,000) because of the more favorable survival rate in developed regions. As a result, breast cancer ranks as the fifth cause of death from cancer overall (458,000 deaths in 2008), but it is still the most frequent cause of cancer death in women in both developing (269,000 deaths, 12.7% of total) and developed regions (189,000) (1). In the United States, during 2011, the estimated new breast cancer cases are 229,060 and the estimated deaths amount to 39,920, for both sexes (breast cancer can also occur in men, although rarely)(2).
Many countries have launched national screening programs for breast cancer awareness and follow-up of subjects with high or middle average risk to develop this disease (e.g., family history of breast cancer, women over 50 years of age, etc.). Mammography is still the only test used for all breast cancer national screening programs; no screening test has ever been more carefully studied than screening mammography. In the past 50 years, more than 600,000 women have participated in 10 randomized trials, each involving approximately 10 years of follow-up (3). The outcome of this assessment is mixed: in a study, the U.S. Preventive Services Task Force estimated the reduction in mortality of approximately 15%-23%. They attributed this improvement mainly to the improvements in screening by mammography (4); but opposite conclusions were derived from other studies, for example (5), where the authors state that despite 30 years of increasingly prevalent use of screening mammograms, the expected mortality benefits have failed to materialize in either trial results or public health data. Moreover, in a Norwegian study the high level of mortality reduction published by the U.S. Services Task Force is challenged (6). The study of Kalager et al. provides additional data pointing at a modest benefit of mammography: making use of the opportunity provided by the systematic screening programs in Norway, the investigators singled out other parameters, such as increased breast-cancer awareness and improvements in treatment. They conclude that the benefit of the Norwegian screening program was small: a 10% reduction in breast-cancer mortality among women between the ages of 50 and 69 years. In this study, with a 10-year course of screening mammography for 2500 women of age 50, the estimated benefit for one woman avoiding to die from breast cancer were contrasted to the estimated harms of up to 1000 women having at least one “false alarm”, about half of whom undergoing biopsy and to 5 to 15 women being misdiagnosed as having breast cancer, and consequently being treated needlessly (7).
These studies emphasize the need for further research into new methods of screening and improved therapy for this important disease that is killing thousands of women worldwide every year. (8)